Add `bootc commit`

Let's consider adding a flow like `podman commit` that creates a bootable container image state from the running host. This would be really useful in concert with a transient rw rootfs as it would allow people to explicitly persist hotfixes where desired.

## Upgrade

This is out of scope.

## Intersection with configmap/layers

The more I think about this the more I feel it intersects with https://github.com/bootc-dev/bootc/issues/22

## Proposed flow example with dnf

```
$ dnf -y install --persist bpftrace
...
Created floating layer: dnf-local
$ bootc status
Booted image: quay.io/exampleos/exampleos@sha256:...
Floating layers:
- bootc-storage:dnf-local (pinned: true)
- registry:quay.io/customer/ca-certificates:latest
$ reboot
... # now i have bpftrace across reboot
$ bootc upgrade
error: Pinned floating layer bootc-storage:dnf-local is not compatible with upgrades
To remove: bootc floating-layers remove bootc-storage:dnf-local
```

But it'd be nice to have a dnf option for this too: `dnf -y remove --bootc-floating-layers`